Lead substitute additives and O2 sensors 5

[NickJ67]

Hi,

Slightly unusual situation here in that we have a couple of 60s Triumph car engines running aftermarket fuel injection, with wideband O2 sensors for tuning and trim, but no catalytic converters.

One of these does not (yet) have hardened exhaust valve seats fitted and has started to experience valve seat recession. I know the correct solution is to have hardened seats fitted. However, for various reasons relating to cost and only needing to get another 9 months / 6k miles from this engine before its complete replacement, we are debating whether we can get away with running an additive to halt (or at least slow) the recession process long enough to get us there.

Up to now we have avoided additives due to worries about killing the O2 sensor. (Bosch LSU 4.2). I've now had a bit of a trawl of the web looking to see whether this is a valid worry and struggling to find anything definitive.

Seems lead does definitely cause premature failure though not instant death. Zinc also gets a mention as being a problem, though I've been running high zinc oils with the same O2 sensor 12 years in the other car without trouble.

The common lead substitutes seem to be using potassium or manganese salts and I can't find much about those. Most, but not all, manufacturers say unsuitable for use with catalytic converters (logically enough!) but nothing about O2 sensors specifically.

Not a mainstream situation I know. Anyone have any specific knowledge or experience?

Thanks & Regards

Nick

 

[BrianPetersen]

If your software has the ability to do so, lock in your current trim settings, disable the self-tune/auto-tune/closed-loop operating mode, and remove the O2 sensors.

This is what is done in the motorcycle world when using aftermarket EFI and the engine is to be operated on race fuel.

 

[TugboatEng]

It seems some of the outboard boat motors with 2-stroke engines had oxygen sensors. I don't see lead substitute being much different from 2-stroke oil.

 

[gruntguru]

There are plenty of products like this around. Link "Safe for oxygen sensors and catalytic converters."

Or you could run a low percentage of leaded fuel. If you visit one of the EFI tuning websites, there are lots of tuners using WBO2 sensors to tune race engines on leaded fuel. They will know how long they last on leaded fuel eg. Link A contaminated sensor will recover significantly by running it for a period in another (unleaded) engine.

je suis charlie

 

[enginesrus]

So where is the data that shows lead oxide deposits on valve contact surfaces and adds protection? Has there been chemical analysis to prove such? Or is it just the ante-detonate doing its normal job and lowering the combustion chamber temperature and thus the valve contact surface temperature causing less supposed micro welding and attack? There is data showing how the leaded gas would chemically attack and shorten valve life.

 

[gruntguru]

The data goes back 100 years. Try Google.

je suis charlie

 

[Lou Scannon]

For example:

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[enginesrus]

All anecdotal information. Tests with no data. "How ever tests at lower speeds valve seat recession was greatly reduced"
So does that mean less load and less heat? The real data shows lead caused the problems, not helping it.

 

[TugboatEng]

Low speeds tend to produce more load and more heat. Reciprocating aircraft engines operate at very low speeds compared to their automotive counterparts which is why they still get to burn leaded gas.

How about this?

"Initial results have indicated that unleaded fuel is more severe than leaded fuel with respect to varnish deposits, full throttle octane requirement increase, exhaust valve seat wear, and wear of certain other engine components."

https://www.sae.org/publications/technical-papers/content/710676/

Then again 2 years later:

" The unleaded gasoline performed as well as or better than a leaded gasoline in this test when both gasolines contained the DC additive. Engine deposits were comparable, and wear and corrosion were reduced when unleaded gasoline was used."

https://www.sae.org/publications/technical-papers/content/720689/

You'll have to fork over some money to get the definition of "wear".

 

[enginesrus]

TugboatEng
That is the problem, we don't know the most important variables. The load and the combustion temperature. Lead had a corrosive effect on valves and seats, the one thing it did good was inhibit combustion or cool it, similar to H2o injection. Hardened seats and valves were desired in the days of TEL through WW2, corrosive resistant materials.
I desire to see the proof of lead deposition onto the valve - seat interface. Who has done the chemical analysis of the lead attachment, and how something corrosive to the valve - seat material is protecting it?

In automobile terms less speed means lower load and temps, throttle is closed some.

Low speeds tend to produce more load and more heat. Reciprocating aircraft engines operate at very low speeds compared to their automotive counterparts which is why they still get to burn leaded gas.

How about this?

"Initial results have indicated that unleaded fuel is more severe than leaded fuel with respect to varnish deposits, full throttle octane requirement increase, exhaust valve seat wear, and wear of certain other engine components."

https://www.sae.org/publications/technical-papers/...

Then again 2 years later:

" The unleaded gasoline performed as well as or better than a leaded gasoline in this test when both gasolines contained the DC additive. Engine deposits were comparable, and wear and corrosion were reduced when unleaded gasoline was used." [end of quote]

What is the DC additive? Of course the hotter burning unleaded is worse.

 

[TugboatEng]

Corrosion from lead certainly seems to be a problem for aircraft engines that operate at high EGT's for extended periods of time.

The principal corrodants in internal combustion engines operated on leaded gasoline are lead oxide, a mixture of sulfates, bromine, and chlorine. The presence of these corrodants have been determined by diffraction, and EDAX deposit analysis. Bench test data has been run to rate various valve materials in these corrosion environments. When the standard line of carbon and nitrogen strengthened stainless steels (such as 21-4N developed specifically for exhaust valve applications) are employed and operating temperatures exceed the capability of these steels, failure results in lead oxide enhanced corrosion fatigue. Nickel-base superalloys, such as Inco-751, possessing excellent lead oxide corrosion resistance are relied upon to extend valve life. Based on lead oxide corrosion bench test data of these alloys, a 115 C increase in operating capability would be expected. However, the life improvement in these alloys is now limited due to sulfidation and bromine/chlorine enhanced corrosion. Consequently, the increase in operating temperature capacity is limited to approximately 60 C.

https://www.osti.gov/biblio/5452230-high-temperature-corrosion-internal-combustion-engine-valves

However, corrosion takes time to occur and may not be the leading contributor to recession, especially for automotive engines that rarely operate at high enough temperatures to cause this corrosion.

Take the lead away and live with detonation at low speeds and see what causes shorter overall engine life.

 

[enginesrus]

Aircraft valves and seats have been made from non corrosive materials for many many years. So then lead not needed for that.
Right on TEL is for anti detonation. It does not coat the valves and seats. Unless there is someone that can show the metallurgical tests to prove it does.

 

[TugboatEng]

Ok, this one shows recession in automotive engines caused by the removal of lead and suggests replacement additives.

"In using unleaded gasoline for cars with soft exhaust valve seats, their recession was found to be excessive after only 3000 - 12 000 km of usage on the highway at 120 km/h "

https://www.sae.org/publications/technical-papers/content/962029/

Aircraft have almost always always had aluminum heads so they've required inserts always. I guess your dilemma comes from two very different uses of lead in two very different applications.

 

[3DDave]

It looks like TEL increases combustion temps or at least interferes with adverse cooler combustion knocking:

https://en.wikipedia.org/wiki/Tetraethyllead[/URL]]A noteworthy feature of TEL is the weakness of its four C–Pb bonds. At the temperatures found in internal combustion engines, (CH3CH2)4Pb decomposes completely into lead and lead oxides as well as combustible, short-lived ethyl radicals. Lead and lead oxide scavenge radical intermediates in combustion reactions. Engine knock is caused by a cool flame, an oscillating low-temperature combustion reaction that occurs before the proper, hot ignition. Lead quenches the pyrolysed radicals and thus kills the radical chain reaction that would sustain a cool flame, preventing it from disturbing the smooth ignition of the hot flame front.

 

[gruntguru]

ABSTRACT
The mechanism of valve seat recession is well
understood and a review of the existing literature shows
that it consists of two processes – the generation of hard
particles that then grind or abrade the valve seats.
Metallic fuel additives can prevent recession by stopping
the generation of these hard particles. Both new and
previously published data are presented to demonstrate
that low concentrations of all the commonly available
additives provide adequate protection for most service
applications. However, the data also show that severe
testing with low treat rates will produce valve seat
recession. The author argues that, if sufficient
concentration of additive is used, the initiation of
recession is stopped under extremely severe conditions
and alternatives to lead can offer complete protection.
The paper concludes that the use of lead replacement
additives should be at the maximum possible level
commensurate with all aspects of engine performance.
There are no standard tests for valve seat recession and,
as a consequence, the additive supplier must be
responsible for recommending dose rates that do not
lead to potentially harmful side effects.

INTRODUCTION
Since their discovery in the late 1920’s, lead alkyls have
been used in gasoline to improve octane quality.
However, environmental pressures have resulted in a
progressive reduction in lead content since the early
seventies, culminating in a complete ban in much of the
European Community from 1 January 2000. As well as
boosting octane, lead acts as a lubricant between the
mating surfaces of exhaust valves and their seats in the
cylinder head. Many older engines took advantage of this
fact and employed “soft” valve seat metallurgy, which
relied on some form of protection to prevent excessive
wear, commonly referred to as valve seat recession.
. . .

je suis charlie

 

[enginesrus]

Again all anecdotal information. Now show the information of how TEL ruined valves and seats, of aircraft engines, especially German engines in WW2!
Wikipedia quotes mean nothing, all that is there is constant repeats of the various wives tails.
Any valve - seat recession is caused by corrosive action and heat. TEL is a known corrosive.
Any tests run on engines that I know of have not identified the important parameters that can cause recession.
Most have just been run for a time on this fuel, then that fuel. Absolutely no information on combustion temperature.
I would like to see the information that shows real data, not a bunch of internet experts.
Data like metallurgical testing etc.
3Ddave if so then it would assist detonation.

 

[TugboatEng]

SAE has that information in the studies I linked. You're going to have to pay to see them. SAE is one of the most authoritative bodies when it comes to engine development. However, you clearly know the answers to your questions so your time is wasted here.

 

[enginesrus]

TugboatEng
Have you looked at that SAE info? I have some old SAE papers I will review. I don't remember ever seeing any sort of report from any organization that mentions metallurgical study's of lead deposition on
Valve seating faces and valve seats. How come all the data about ruined valves and seats caused by TEL is almost completely ignored by all the supposed experts in the engine field? I'm not anti TEL. I'm just interested in real information and not the internet story's passed on about the subject.

 

[TugboatEng]

I think you need to look at the fields the experts are working in. The aircraft experts talk about valve recession caused by lead while the automotive experts talk about valve recession due to no lead. These are two very different applications.

 

[Lou Scannon]

It would also be worthwhile to research the reasons that US auto manufacturers started manufacturing cylinder heads with induction hardened exhaust valve seats in the early 1970s, and why automotive engine repairs and overhauls in the past several decades frequently include installation of stellite exhaust valve seats. Let me know if you think the money spent on these upgrades was wasted, and why.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz